Describe an experiment to demonstrate electromagnetic induction. Explain the principles behind the phenomena. What variations in your experiment can you include to demonstrate the factors which affect the magnitude and the direction of the induced emf.

When a magnet is pushed into the solenoid, there is a change in magnetic field lines linking the solenoid, which produces an induced e.m.f. This induced e.m.f. drives a current in the circuit, causing the pointer of the galvanometer deflects momentarily.

When the magnet is stationary, there is no change in magnetic field lines linking the circuit. There is no induced e.m.f. and hence no current detected by the galvanometer.

The experiment show that induced current (or induced emf) is produced in the coil due to the changing magnetic field in the solenoid. This process is called electromagnetic induction.

The factors affecting the magnitude of the induced emf can be demonstrated as follows:

o When the magnet moves at a faster speed in or out of the coil, the magnitude of the induced current is increased.

o When a stronger magnet is used, the magnitude of the induced current is increased.

o When the number of turns in the coil is increased, the magnitude of the induced current is increased.

2.

With the aid of a diagram, describe the structure of an a.c. generator and explain how it works.

Structure

An a.c. generator consists of a rectangular coil of wire connected to a pair of slip rings. Each slip ring is in contact with a carbon brush and the carbon brushes are connected to an external circuit.

The rectangular coil is placed between the opposite poles of a magnet.

How it works

When a coil is rotated, the magnetic field flux through the coil changes and e.m.f is induced in the coil.

The induced e.m.f generated drives a current through the external circuit.

3.

What are the functions of the slip rings and the carbon brush of an a.c. generator?